NSAIDS have antipyretic activity and can be used to treat fever. [75] [76] Fever is caused by elevated levels of prostaglandin E2 , which alters the firing rate of neurons within the hypothalamus that control thermoregulation. [75] [77] Antipyretics work by inhibiting the enzyme COX, which causes the general inhibition of prostanoid biosynthesis ( PGE2 ) within the hypothalamus . [75] [76] PGE2 signals to the hypothalamus to increase the body's thermal set point. [76] [78] Ibuprofen has been shown more effective as an antipyretic than paracetamol (acetaminophen). [77] [79] Arachidonic acid is the precursor substrate for cyclooxygenase leading to the production of prostaglandins F, D & E.